This invention pertains to a process for catalytic hydroconversion of petroleum residua feedstocks to produce lower boiling hydrocarbon liquid products. It pertains particularly to such a hydroconversion process in which the separated and pressure-reduced liquid fraction is treated so as to avoid precipitation of contained asphaltene compounds in downstream processing equipment and provide sustained high conversion operations.
The catalytic hydrogenation of petroleum residua feedstock in an ebullated-bed reactor is well known. In U.S. Pat. No. Re. 25,770 to Johanson, a process is disclosed whereby the ebullated bed catalytic reactor is used to accomplish hydroconversion of material boiling above 975.degree. F. in an expanded catalyst bed to produce lower boiling distillates, the catayst particles being maintained in random motion by upward flow of the reactants. The recycle of reactants boiling above about 680.degree. F. to the reaction zone is disclosed in U.S. Pat. No. 3,412,010 to Alpert, et al. The recycle of such heavy fractions permits operation at high levels of conversion of the 975.degree. F..sup.+ material, and permits such operation at higher reactor space velocity if the recycle consists primarily of material boiling above about 875.degree. F. Also, moderate conversion of petroleum residua feedstocks to remove asphaltenes prior to desulfurization is disclosed in U.S. Pat. No. 3,948,756 to Wolk et al. It has been known that operations on petroleum residua at high hydroconversion levels, i.e., above about 75 V %, are not sustainable when the depressurized vaporous and liquid effluents from the catalytic reactor are permitted to mix under conditions of cooling to below about 750.degree. F., as disclosed in U.S. Pat. No. 3,338,820 to Wolk et al. However, it has been observed that for conversions above about 85 V % this arrangement does not result in sustained operations. These high conversion conditions cause precipitation of asphaltenes in a meso-hpase which fouls and can even plug the downstream equipment, and when recycled to the reactor such asphaltenes cause the catalyst bed to agglomerate and defluidize. A long-sought solution to this asphaltene precipitation problem is advantageously and unexpectedly provided by the present invention.